Use JSON as format for .HA_RESTORE (#129792)

* Use JSON as format for .HA_RESTORE

* Adjust bakup manager test

homeassistant/components/backup/manager.py

@@ -308,7 +308,7 @@ class BackupManager(BaseBackupManager):
         def _write_restore_file() -> None:
             """Write the restore file."""
             Path(self.hass.config.path(RESTORE_BACKUP_FILE)).write_text(
-                f"{backup.path.as_posix()};",
+                json.dumps({"path": backup.path.as_posix()}),
                 encoding="utf-8",
             )